China is a colossal country and, as befits such a global powerhouse, it has made some colossal mistakes. Take its infamous one-child policy, implemented in 1979 and condemned from that day forward. A new study released in Science makes it clear just how misguided the idea was.

Initially, the policy seemed to make a cold kind of sense: the country’s population growth was out of control, leaping nearly 75% from 1949 to 1976; its per capita income was about 300 yuan, or just over $48, and families with multiple children had nowhere near enough money to raise them well. Why not just clamp down on all the prodigious baby making and solve both problems at once?

Thirty-four years later, the planners can claim a crude victory. China’s economy has boomed, and its 1.34 billion population is estimated to be about 15% smaller than it would have been otherwise. But that means that 250 million Chinese babies who would have been born never were. Until 2004, when the practice of sex-selective abortion was banned, millions of girls were aborted to satisfy China’s traditional preference for boys; and as a result of that gender bias, there are 32 million more marriage-age men in the country than there are women, according to the British Medical Journal.

Lost in all those troubling numbers is what’s become of the singletons themselves. Just 27% of those born in China in 1975 were only children; in 1983, it was 91%. When you’re your parents’ one shot at a genetic legacy, you may get to attend all the best schools, wear all the best clothes and eat all the best foods — at least relative to children in multiple-sibling households. But you also wind up with an overweening sense of your own importance. For years now, Chinese parents and teachers have lamented what’s known as the xiao huangdi — or little emperor — phenomenon, a generation of pampered and entitled children who believe they sit at the center of the social universe because that’s exactly how they’ve been treated.

In 2004, Fortune magazine explored the problem, interviewing teachers and employers who complained that one-child-policy babies never learn how to “eat bitterness” — or cope with disappointment and frustrations in ways that would better prepare them for life. Said one kindergarten director:

Kids these days are spoiled rotten. They have no social skills. They expect instant gratification. They’re attended to hand and foot by adults so protective that if the child as much as stumbles, the whole family will curse the ground.

In China today, some employers have gone so far as to specify “no single children” in job postings. In 2010, one branch of government, the Chinese People’s Political Consultative Conference, called on party leadership to abandon the one-child policy — a surprising bit of bureaucratic assertiveness in so top-down a country.

But is the little-emperor label fair? As I reported in my book The Sibling Effect, most studies show that in the U.S., only children don’t suffer from their singleton status and even typically wind up outperforming other children on a range of measures, including vocabulary, academic performance, sense of humor, the ability to focus on tasks and — never mind the stereotypes — getting along with others. But those are kids who grow up in a culture with a whole mix of family types, who learn that whatever extra pampering they get from their parents is not what all kids get, and that they’re no more entitled to privilege than anyone else. In the singleton hothouse of China, the Science paper makes clear, things are very different.

The study, conducted by a team of researchers from various Australian universities, compared 421 young adults in China divided into two groups: those born just before the one-child policy was imposed and those born just after. The oldest members of the sample group were 37, the youngest were 29.

The investigators asked the subjects to play four social-experiment games known as the dictator game, the trust game, the risk game and the competition game. In the dictator game, participants are paired off with an anonymous partner, and one is given the equivalent of $30 and allowed to give any, or none, of that amount to the other partner and keep the rest. Then they are paired with new anonymous partners and the roles are reversed. The trust game involves something similar, but the giver sends either no money or whatever money he decides to part with to the receiver, and the receiver then has the opportunity to give some of it back to the same person. In the risk game, individual participants are given a sum of money and allowed to wager as much or as little as they want on a coin flip that has a 50-50 chance of either tripling their bet or leaving them with nothing. Finally, the competition game requires subjects to perform a mathematical exercise — adding up randomly generated numbers while being graded for speed and accuracy. They have the choice of either being paid a small amount for every correct answer or 10 times that amount if they compete with another player in the room and win. If they lose, they get nothing.

In two of the four tasks, the one-child subjects behaved just as would be expected of an entitled, narcissistic birth cohort. They were less generous in the dictator game, passing on 40.1% of the money, compared with the 43.4% those born before the one-child policy gave away. In the trust game, they both sent less to the other player (46.1% vs. 50.6%) and returned less (30.4% vs. 35.4%) — figures suggesting a lack of faith that any altruistic behavior on their part would be reciprocated.

The other two results were a bit harder to parse: the one-child subjects were less competitive than those born earlier, with 44.2% of them choosing to compete in the math exercises, compared with 51.8%. The only children also scored lower in the risk game, with 58.1% wagering triple or nothing on the coin flips, compared with 66.4% of those with siblings. But in neither case, the researchers found, were those choices signs of healthy humility and cautious wisdom. Rather, they were simply symptoms of pessimism — and worse.

In personality tests administered after the games, one-child subjects scored much lower when asked to rate, on a scale of 0 to 100, whether they believed the sun would be shining the next day. In a 44-question personality survey, they also scored worse on a whole range of metrics including agreeableness, openness, extraversion, neuroticism and pessimism again. All this, the researchers concluded, “is consistent with the finding that positive sibling relationships moderate the relationship between stressful life events and internalizing behaviors.”

The hard irony for the parents of one-child-policy offspring — to say nothing of those singletons themselves — is that the entire suite of less adaptive traits they exhibit in the study not only doesn’t improve their prospects in life but actually diminishes them. Every one of those attributes has been linked directly to poorer outcomes in educational and professional achievement, individual health and stability in marriage. The one-child policy, which the researchers call “one of the most radical approaches to limiting population growth,” has in all respects, except the mere birthrate numbers, been a hash of unintended consequences.

For now, the one-child policy is still in place, but like any such ill-considered experiment in social engineering, it is being increasingly flouted, especially outside major cities like Beijing and Shanghai. Even senior communist officials have suggested that the rule could be scrapped as soon as 2015. That would be a welcome — and long overdue — change, as one more regime learns one more time that there are some places policymakers simply shouldn’t tread.